Children's Cancer Study Group is engaged in carrying out clinical research studies which have been developed by senior investigators in the group and approved by the NCI. These programs, which are designed to improve the care and survival of children with leukemia and solid tumors, include both Phase II and Phase III studies. Phase II studies are primarily those involving new agents which have completed Phase I trial. The current study for children with newly diagnosed acute lymphocytic leukemia involves stratification at diagnosis based on white blood count, age, and cell morphology. Remission is induced with prednisone, vincristine and L-asparaginase in all children and similar CNS prophylaxis is given to all except the good risk group which is randomized to either intrathecal methotrexate or cranial irradiation and intrathecal methotrexate. All patients are then randomized for various maintenance programs to answer whether it is advantageous to 1) give further intermittent intrathecal methotrexate and 2) various intermittent additive drugs to systemic chemotherapy with daily 6-mercaptopurine and weekly methotrexate orally. Children with acute non-lymphocytic leukemia are induced with continuous infusion cytosine arabinoside for 7 days plus 3 daily doses of adriamycin, given at 2 week intervals. If remission is obtained, children with HLA sibling matches will receive bone marrow transplant. Those without will enter a chemotherapy maintenance program involving a cyclic versus continuous use of multiple agents. Solid tumor studies include the intergroup studies for Wilms' tumor, Ewing's sarcoma and rhabdomyosarcoma. Studies for Stage I and II Hodgkin's disease and non-Hodgkin's lymphoma are being done in conjunction with other cooperative groups. Other Children's Cancer Study Group studies are current for brain tumors, osteogenic sarcoma, histiocytosis X, retinoblastoma, liver tumors and ovarian tumors.